1. Field of the Invention
This invention relates to fiber couplers. More particularly, this invention relates to fused fiber couplers and methods especially relating to fused fiber couplers having a coupling region including a bend.
2. The Prior Art
With the increase in throughput required for today""s communications technology has come the need for better, faster, smaller, less costly, fiber optic devices due to fiber optics advantages over various other media. Because of these needs, the advantage of fused fiber couplers has become increasingly evident.
More recently, the fused biconical taper technique for forming fiber optical couplers including Wavelength Division Multiplexers (WDM) has proven advantageous as well, as described and applied in U.S. Pat. No. 5,809,190 in a Dense Wavelength-Division Multiplexer (DWDM) application. Though advantageous, the technology described in U.S. Pat. No. 5,809,190 is burdened by size constraints. That is, fused Wavelength Division Multiplexers having a pair of pigtail ends on opposed sides of the WDM is a geometric problem in need of a solution. Having to cope with the geometry of such WDMs limits the spatial utility of such devices especially when one attempts to implement them in a WDM tree arrangement.
Furthermore, miniature single fiber bend devices have proven useful in allowing tighter bends to be accomplished as described in U.S. Pat. No. 5,452,393. However, such single fiber techniques have very limited utility.
Therefore, it is an object of the present invention to overcome the shortcomings of the prior art by providing a fiber optical coupler capable of achieving tight bends in the coupling region and thereby, changing the direction of the light path in the coupling region and the layout of the pigtail ends to a single side of the coupler. Disclosed herein, then, is an inventive microbend fused coupler.
To overcome these and other shortcomings of the prior art, disclosed herein is a fused fiber optical coupler including a bend in the coupling region. By utilizing a fused biconical taper technique to form the coupling region and thereafter bending the fibers in the region of reduced diameter, a microbend coupler may be achieved resulting in not only a tension-free coupling region, but also a fused fiber coupler of shortened length including pigtail ends all emanating from one side of the fused fiber coupler. Such fused fiber couplers are more stable, smaller, and more flexible for optical applications.
More particularly, a Microbend Fused-Biconical Tapered (FBT) fiber coupler is disclosed. The fused bend area is comprised of a pair of optical fibers heated, twisted and fused together in a coupling region. The fibers include cladding covered cores. In the coupling region, a uniform biconical taper is present, converging from the two ends of the coupling region to a middle section having a reduced diameter as compared to the starting fiber core diameter. The taper angles at each respective end of the coupling region are complimentary. A bend of a minimized radius of curvature is created about a center point of the lesser diameter coupling region. The result is a 2xc3x972 or 1xc3x972 fused fiber coupler having two branch channels which may occupy a lesser spatial area than conventional non-bent couplers. Because the birefringence of the coupler resulting from the progressive stretching is subsequently nulled-out by twisting of the coupling region, the resulting fused fiber coupler includes very low polarization dependence.
The method of forming the microbent fused fiber coupler includes providing two fibers having been stripped of their plastic coatings at a midsection. The two fibers are arranged in parallel and the stripped portions where the plastic coating layer is removed are oriented next to each other. Once the fibers are held in side by side orientation by holding devices, the holding devices pull the fibers axially and force the substantially bare midsections toward one another, preferably by twisting the fibers about one another one time. The two fibers are, thus, in contact with each other and are heated using a gas burner or electric heater. Thereafter, the exposed fiber sections are softened causing their claddings to fuse. Pulling on the softened fibers forms a biconical taper at each of the four ports, a desirable mode interference occurs, and resulting desirable characteristics of fused fiber couplings are present. By then rotating the holding device approximately 180xc2x0, and then adhering both ends of the fused region to a substrate, a substantially U-shaped bend in the fused coupling region is formed. The substrate with the adhered microbent fused fiber coupler is then encapsulated within an appropriate confinement.
It is therefore an object of the present invention to provide a 2xc3x972 microbend fused fiber coupler wherein the transmission direction of output light is in a direction opposed to the transmission direction of the input light.
It is another object of the present invention to provide a microbend fused fiber WDM with an environmentally stable passband.
It is yet another object of the present invention to provide a least radius of curvature bend FBT coupler.
It is another object of the present invention to provide a method for forming a microbend FBT coupler.
It is yet another object of the present invention to provide a microbend FBT coupler with very high uniformity of insertion loss of multipassband as a coupler.
Viewed from a first vantage point a fiber optic coupler is disclosed, comprising, in combination: a first fiber; a second fiber; and wherein said first fiber and said second fiber are fused together in a bend region.
Viewed from a second vantage point a fiber optic light routing device is disclosed, comprising, in combination: a pair of light path inlets; a pair of light path outlets; and a bent multiplexing light path oriented between said light path inlets and said light path outlets, said bent multiplexing light path comprising the union of said light path inlets and outlets.
Viewed from a third vantage point a method of forming a fiber optic coupler is disclosed, the steps comprising, in combination: orienting substantially exposed regions of optical fibers side by side; heating and stretching the substantially exposed regions; and bending the exposed region.
Viewed from a fourth vantage point a Wavelength Division Multiplexer is disclosed, comprising in combination: a first pair of fiber pigtails transitioning into a first Y-shaped jumper; a second pair of fiber pigtails transitioning into a second Y-shaped jumper; and a biconically tapered fused bend region interposed between said first Y-shaped jumper and said second Y-shaped jumper.
Viewed from a fifth vantage point a method of forming a microbend Wavelength Division Multiplexer is disclosed, comprising the steps of: providing a plurality of lengths of low loss optical fibers; removing the plastic coating of the fibers at a midsection of the fibers; arranging the skinned fiber midsections in a side by side contact area; heating and stretching longitudinally in a portion of said contact area to form a coupling region; terminating the heating and stretching step once a predetermined passband spacing is obtained; twisting and reheating said coupling region until maximum isolation and minimum insertion loss are obtained; bonding the fused fiber at one end outside of the coupling area to a substrate; rotating the substrate to form a bend in the coupling area; bonding the fused fiber at the other end outside of the coupling area to the substrate; annealing the bend area; trimming the passband spacing and wavelength; and encapsulating the bonded fused fibers and substrate combination within a confine.